1. Field of the Invention
The present invention relates to a power semiconductor device with SOI (Silicon On Insulator) structure.
2. Discussion of the Background
In recent years, integrated circuits (ICs) each having a large number of transistors and resistors which are connected to make an electric circuit and integrated on one chip are widely used in important portions of computers or communication devices. Among the above ICs, an IC of a type containing a semiconductor device with high withstand voltage (power semiconductor device) is called a power IC.
FIG. 1 is a cross sectional view showing the internal structure of a conventional power semiconductor device (pin diode) with SOI structure.
In FIG. 1, a reference numeral 91 denotes a semiconductor substrate, and an i-type semiconductor active layer (SOI semiconductor layer) 93 of low impurity concentration is formed above the semiconductor substrate 91 with an insulative film (SOI insulative film) 92 disposed therebetween.
An n-type emitter layer 94 of high impurity concentration and a p-type emitter layer 95 of high impurity concentration are formed by diffusion in the surface area of the i-type semiconductor active layer 93. A cathode electrode 96 is formed on the n-type emitter layer 94 and an anode electrode 97 is formed on the p-type emitter layer 95.
According to the power semiconductor device with the above structure, an applied voltage is shared (distributed) between the main body of the device and the insulative film 92 and thus a voltage applied to the main body of the device is lowered so that a high withstand voltage can be attained.
However, this type of power semiconductor device has the following problem. Since the voltage which the insulative film 92 can share is limited, it becomes difficult to attain a higher withstand voltage with the conventional structure.